Heretofore, the drive power transmitting mechanisms of automobiles employ a constant-velocity joint for connecting a transmission shaft to another transmission shaft to transmit rotational power to axles.
FIG. 20 shows in cross section a part of a conventional constant-velocity joint 2 of the above type (see Japanese Laid-Open Patent Publication No. 10-184717).
The constant-velocity joint 2 comprises a tubular outer member 4 connected to a transmission shaft and an inner member 6 inserted in the outer member 4 and connected to another transmission shaft. The outer member 4 has three axially extending guide grooves 8 defined in an inner circumferential surface thereof. The inner member 6 has three trunnions 10 projecting respectively into the guide grooves 8. Rollers 14 are mounted on the respective trunnions 10 by needle bearings 12. The rollers 14 rollingly engage in the guide grooves 8 of the outer member 4.
With the conventional constant-velocity joint 2, in order to hold the needle bearings 12 against dislodgment from the rollers 14, circular grooves 16 are defined in the inner circumferential surfaces of the rollers 14, and the needle bearings 12 are press-fitted in the respective grooves 16.
For mounting a needle bearing 12 in a groove 16, all its needle bearing rollers except one needle bearing roller are annularly arrayed in and along the groove 16, and then the remaining needle bearing roller is press-fitted according to the keystone effect. In order to retain the needle bearing rollers neatly in the groove 16, the needle bearing rollers and the groove 16 need to be machined precisely for minimizing the tolerances of the dimensions of the groove 16 and the dimensions of the needle bearing rollers.
When a groove 16 is to be formed in the inner circumferential surface of a roller 14, since flanges 17a, 17b are to be provided on both sides of the groove 16, a machining tool is inserted into the groove 16 and cuts the groove 16. Chips produced when the groove 16 is cut need to be reliably discharged. Therefore, the machining process is highly difficult to perform.
Japanese Laid-Open Patent Publication No. 10-184717 discloses a technique for forming a round hole free of the flanges 17a, 17b and thereafter bringing two washers into engagement with the inner circumferential surface as a substitute for the flanges 17a, 17b, rather than forming the groove 16 in the inner circumferential surface of the roller 14. Though the round hole itself can easily be machined, it is necessary to machine engaging grooves where the washers are placed to engage the inner circumferential surface of the roller 14. It is also necessary to perform a process of bringing the washers into the engaging grooves.
In an attempt to solve the above problems, HONDA MOTOR CO., LTD. has proposed a constant-velocity joint 18 having a structure shown in FIG. 21 (see Japanese Laid-Open Patent Publication No. 11-210776).
The constant-velocity joint 18 includes an inner member 6 including a trunnion 10 with a larger-diameter portion 19 disposed on its proximal end. A roller 14 has a flange 17a disposed only on an end of the inner circumferential surface thereof in the direction in which the trunnion 10 projects.
With the above structure, the chips can easily be discharged when the inner circumferential surface of the roller 14 is machined or processed. A needle bearing 12 mounted between the trunnion 10 and the roller 14 is held in position between the flange 17a of the roller 14 and a step 20 provided by the larger-diameter portion 19 of the inner member 6.
Another conventional constant-velocity joint of this type is shown in FIG. 22 (see Japanese Laid-Open Patent Publication No. 2001-208090).
As shown in FIG. 22, the constant-velocity joint has a roller mechanism 26 including a retaining ring 24 retained by a circumferential groove 23 and mounted on an axial end of a cylindrical inner circumferential surface 22 of a roller 21, and a retaining flange 25 disposed on the other axial end of the cylindrical inner circumferential surface 22 and integrally formed with the roller 21.
A plurality of needle rollers 27 are mounted on the cylindrical inner circumferential surface 22, and held in place by a support ring 29 that is fitted over the outer circumferential surface of a trunnion 28.
With the roller mechanism 26 disclosed in Japanese Laid-Open Patent Publication No. 2001-208090, the retaining ring 24 is disposed at a distal end 28a of the trunnion 28, and the retaining flange 25 is disposed at a proximal end 28b of the trunnion 28.